Note: Descriptions are shown in the official language in which they were submitted.
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21.2.79 1 P~IN 9108
Method of providing an epitaxial la~er.
The invention relates to a method of providing
an epitaxial laycr from a gaseous phase on a substrate,
in which a susceptor ia which the substrate is heated
is provided with a layer of tho same ma-terial as that
of which the substrate consists, on which layer the sub-
strate is provided, aft~r which an etchant is passed
over the subs-trate so that the side of the substrate
remote from the susceptor is etched and chemical -trans-
port of the said material takes place from the susceptor
to the side of the substrate facing the susceptor, and
the epitaxial layer is then deposited on the side of thc
substrate~remote from the susceptor.
~ method of the kind mentioned in the preamble
is known ~rom J. Electrochem. Soc. Vol. 122,
15 1705 - 1709 (1975).
When depositing an epitaxial layer of semi-
conductor material on a substrate of semiconductor
material comprising a volatile dopant, atoms of said
dopant may diffuse out of the subs-trate and land in the
gaseous phase. During the deposition said atoms are in-
corporated in the epitaxial layer and influence the
resistance of the layer This phenomenon is known as
the au-todope effect.
In order to prevent this effec-t, special
measures have t-o be taken when depositing an epitaxial
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21.2.79 ~ ~ PI~ 9~08
layer on a substrate comprising a volatile dopant.
For example, a method is used in which the
substrate consisting, for example, of silicon is provid-
ed, prior to the epi-taxial deposition~ on the side not
to be covered by epitaxy with a layer masking against
out-diffusion, for example~ of silicon dioxide or silicon
nitride. This is a rather cumbersome method in which
moreover the possibility exists that crystal defects
are introduced.
The method mentioned in the preamble yields
reproducible results only if an epi-taxial layer is de~
posited the resistivity of which need not exceed 10 to
15~2 cm.
One of the objects of the invention is to pro-
vide a si.mple and reliable method in which a high-resi.st-
ance epitaxial layer can be growrL irL a reproducible man-
ner on a substrate having a comparatively very low
resistance.
The invention is inter alia based on the re-
cognition of the fact that an i.mportant improvement can
be achieved if the side of the substrate remote from thesusceptor is also provided with a layer maskirLg against
out-diffusion.
This is achieved by means of the method men-
tioned in the preamble when, according to the invention,
it is characterized in that the passing-over of the
etchant is carried out in two steps, between which two
steps an epitaxial growth step is introduced, and that
during the second etching step the material deposited on
the side of the substrate remote ~rom the susceptor dur-
ing the said growth step is removed partly an~ the
material obtained by chemical -transport on the side of
the substrate facing the susceptor reaches a desired
thickness.
The growth of an epitaxial layer of high
resistance can be continued on the part of the epitaxial
layer remaining on the side of the substrate remote from
the susceptor after the second etching step, whi.ch part
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21.2.79 3 PHN 9108
compriscs a considerably smaller amount of the volatile
dopant than the substrate, since from that instant the
substrate is shielded from the surrounding gaseous phase.
In the method according to the invention a
substrate is preferably used which consists of silicon
and an epitaxial layer of silicon is deposited and the
substrate comprises arsenic or boron as a dopant. For
example~ an epitaxia~ layer having a high resistivity
up to 100~ cm can be grown on an arsenic-doped substrate
10 having a resistivity of 1-3.10 3Q cm in a reproducible
manner and with comparatively few crystal defects.
Particularly good resul-ts are obtained if
during the second etching step 0.2 - 0.4/um of the
material deposited during the said growth step re-
mains.
The invention will ~ow be described iIl greaterdetail with reference to an embodiment and the accom-
panying drawing, in which
Fig. 1 is a diagrammatic sectional view o~
an epitaxial reactor in which the method according to
the invention is carried out, and
Fig. 2 is a diagrammatic sectional view of a
device in a stage of rnanufactu:re by means of the method
accordi~g to the invention.
Figure 1 shows a reactor having a quartz tube
9 and a high-frequency induction coil 10 by whlch a
temperature is generated in a graphite susceptor 4
which is higher than that of its ambience.
As a result of this, a method can be per- ;
formed in said reactor for providing an epitaxial layer
1, 2 (see also Fig. 2) from a gaseous phase on a sub-
strate 3, the susceptor 4 v~ which the subs-trate 3 is
heated being provlded with a layer 5 of the same material
as that of which the substrate 3 consists.
The substrate 3 is provided on the layer 5
a~ter which an etchant is passed over the substrate 3
so that the side 6 of the substrate 3 remote from the
ausoeptor ZZ ~ 9 etched and chemlcal tr~nsport Or the sald
1.
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63~j~
21.2 79 4 ~IIN 9108
matarial takes place from the susceptor ll to the side
7 of the substrate 3 facing the susceptor l~.
The epitaxial. layer 1, 2 is then depos.ited on
the side 6 of the substrate 3 remote from the susceptor
4.
~ ccording to the invention the passing-over
of the etchant is carried out in..two steps, between
which two steps an epitaxial growth step is introduced.
During the second etching step the material deposi.ted
on the side 6 of the substrate 3 remote from the suscep-
; tor 4 during the said growth step is removed partly and
the material ~ obtained by chemical transport on the
side 7 of the substrate 3 facing the susceptor 4 ob-
tains a desired thickness.
Starting material, for example~ is a d:Lsc-
shaped silicon substrate-3 having a diameter of 7.5 cm,
a thicl~ness of 420/urn and a doping of arsenic atorns of
3.5010 9 per cm3 (resistivity 1.7.10 3 ~ cm). A 10/um
: thick layer 5 of polysilicon is provided on the susceptor
in a usual manner.
During the first etching step there is etched
for 2 minutes with 1 percent hydrogen chloride in hydro-
gen at -approximately 1200 C. During this step approxi-
mately 0.41um is etched from the side 6 of -the substrate
3 and a 2/u~m thick layer is transported from the layer
: 5 to the si.de 7.
During this etching treatment, arsenic is re-
leased in the apparatus.
The said transport takes place under the in-
fluence of an approximately 15 C temperature diff`erence
between the susceptor l~ and the substrate 3.
~ rinsing treatment with hydrogen at 1200C
for 5 minutes is then carried ou-t and the temperature
is reduced to 1150C.
In the subsequent growth step, a 1.3/um thick
epitaxial layer is deposited on the side 6 of the sub-
strate from a gaseous mixture of trichlorosilane
(Si~Cl3) and hydrogen in a usual manner at 1150~C. ......
... ... . . ,, . . .. . _ , .. . . .. ........ . . . . .. .. .... .. .. ... . .. . ..
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21.2.79 5 PHN 910~
In the last-mentioned layer a concentration o~ arsenic ...
atoms usual in known methocls is i.ncorporated from arsenic
atorns present in the apparatus and still diffusing out
of the substrate. The thickness of the layer 8 increases
only slightly.
Another rinsing treatment with hydrogen for
5 minutes is then carried out while the temperature is
raised to 1200C.
In the second etching step there is then etched
for 5 minutes w:ith 1 percent hydrogen chloride in hydro-
gen at approximately 1200C. During this step, so much
of the epitaxial layer of the side 6 of the substrate
is etched away that a 0~3/um thick layer 1 remains.
This layer 1 serves as a mask against out-dif~usion
during the subsequent epitaxial growth on the side 6
of the substrate 3.
During -this etching step, less contamination
o.f the apparatus occurs than in the first etching step,
since the arsenic concentration of the layer to be
etched is lower than that of the substrate.
During this etching step the layer 8 obtains
a thic.kness of approximately 7/um.
Subsequently there is rinsed with hydrogen
` for 5 minutes and the temperature is decreased ~rom ,
25 1200C t.Q 1~150~. ,
An epitaxial layer 2 of a desired thickness
is then grown at 1150 C from a usual gas mixture of
trichlorosilane and hydrogen. This layer is little con-
taminated with arsenic and has a resistivity of 100 - 300
ohm cm without any addition.
By the addition of phosphine (PH3) to the
epitaxial gas mixture, the layer 2 may be given a
desired resistivity below lO0 ohm cm.
By the addit~.on o~ other dopants the layer 2
may also be given another conductivity type with the
desired resistivity.
Epitaxial gas mixture o-ther than those mention
ed may also be used~ as well as other substrat~s, for
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21.2.79 6 PHN 9108
example doped with boron (resistivity 10-20.10 3Q crn)0 -
Frorn this it will be obvious that many varia-
tions rnay be used without departing ~rom the scope of
thi.s invention.
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